Objectives: Breath-stacking asynchrony during assist-control-mode ventilation may be associated with increased tidal volume and alveolar pressure that could contribute to ventilator-induced lung injury. Methods to reduce breath stacking have not been well studied. The objective of this investigation was to evaluate 1) which interventions were used by managing clinicians to address severe breath stacking; and 2) how effective these measures were.
Setting: Sixteen-bed medical ICU.
Patients and interventions: Physiological study in consecutively admitted patients without severe brain injury, who had severe breath stacking defined as an asynchrony index greater than or equal to 10% of total breaths. During 30 minutes before (baseline) and after any intervention employed by the managing clinician, the ventilator flow, airway pressure, and volume/time waveforms were continuously recorded and analyzed to detect normal and stacked breaths. The initial approach taken was assigned to one of three categories: no intervention, increase of sedation-analgesia, or change of ventilator setting. Nonparametric Wilcoxon-Mann-Whitney tests and multiple regression were used for statistical analysis. Quantitative data are presented as median [25-75].
Main results: Sixty-six of 254 (26%) mechanically ventilated patients exhibited severe breath-stacking asynchrony. A total of 100 30-minute sequences were recorded and analyzed in 30 patients before and after 50 clinical decisions for ongoing management (no intervention, n=8; increasing sedation/analgesia, n=16; ventilator adjustment, n=26). Breath-stacking asynchrony index was 44 [27-87]% at baseline. Compared with baseline, the decrease of asynchrony index was greater after changing the ventilator setting (-99 [-92, -100]%) than after increasing the sedation-analgesia (-41 [-66, 7]%, p<0.001) or deciding to tolerate the asynchrony (4 [-4, 12]%, p<0.001). Pressure-support ventilation and increased inspiratory time were independently associated with the reduction of asynchrony index.
Conclusions: Compared with increasing sedation-analgesia, adapting the ventilator to patient breathing effort reduces breath-stacking asynchrony significantly and often dramatically. These results support an algorithm beginning with ventilator adjustment to rationalize the management of severe breath-stacking asynchrony in ICU patients.